1. Technical Field
The present invention relates to methods and apparatus for separating solids from liquids and other solids and, in particular, to dewatering and decontaminating coal tailings, clean coal products, and mineral slurries. The present invention also relates to methods and apparatus for liquid purification and, in particular, to methods and apparatus for recovering decontaminated process water from coal tailings, clean coal products and mineral slurries.
2. Background Information
In the cleaning or washing of coal for commercial use as a fuel and the like, the uncombustible ash content of coal is usually removed to enhance the heat content of the coal. Reduction in the ash content results in savings in transportation and ash disposal costs. Other materials frequently occurring with coals that may be removed in washing operations include various clays and sulfides. Such clays commonly include aericite (KAl2(AlSi3O)(OH)12, smectite (Al2Si4O10(OH12)H2O, and kaolinite clays (Al2Si4O5(OH)4. Sulfides are usually pyrite (FeS4(isometrical)).
During the processing of coal to effect such washing, a coal refuse slurry is generated. This slurry comprises coal fines known as tailings, and contaminants such as clay and mud suspended in plant process water. Due to the high volume of water used in the processing of coal, it is necessary to reclaim the wash water for recirculation in the plant. The concentrated solids are sent to an impoundment pond for disposal. In some cases in which coal washing plants have been operating for years, such slurry ponds may occupy hundreds of acres and may contain millions of tons of coal fines. These slurry ponds may also contain coal slurry to a depth of 70-150 feet. Such slurry ponds not only occupy a great deal of valuable land, but they also contain a considerable amount of energy and water resources.
Clean coal slurries are also used as, for example, an effective and cost effective means for transporting coal over distances from the place of production to the place of use.
The prior art discloses various methods and apparatuses for dewatering and decontaminating refuse pond coal slurries and for dewatering clean coal slurries.
U.S. Pat. No. 4,128,474 to Ennis discloses a wet mechanical process for cleaning, upgrading and dewatering fine coal. The process provides for forming an aqueous feed slurry of fine coal and its associated contaminant particles wherein all particles have a particle portion size of less than about 6 mm. ranging to zero. The feed slurry is separated into coal slurry and refuse slurry portions in a spiral gravity concentrator by removing contaminants having a particle size greater than about 0.15 mm. The concentrated coal slurry is then fed to a hydrocyclone separator where all the. ultra-fine silt material having a particle size of less than 0.15 mm. is removed and the coal particle fraction 6 mm. to 0.15 mm. is accumulated and thoroughly dewatered.
U.S. Pat. No. 4,257,879 to Bogenschneider, et al. discloses a coal slurry dewatering process in which the fine grain content is regulated to keep the filter cake at a constant level. A separation of the slurry into a predominantly relatively fine grain fraction and a relatively coarse grain fraction, with the division point being between about 0.03 and 0.15 mm. is carried out with a formation. if a coal agglomerate from the fine grain fraction is accomplished.
U.S. Pat. No. 4,526,121 to Shudo, et al. discloses a ship for treating a coal slurry comprising a pair of opposed trays disposed in the vicinity of the upper deck for causing the coal slurry supplied thereto to flow forward and delivering the slurry, a slanting dewatering screen disposed below each of the trays for dewatering the coal slurry delivered from the tray to separate a particulate coal fraction having relatively large particle sizes and conveyors for transporting to a specified position on the upper deck the particulate coal fraction dewatered and falling off the screen.
U.S. Pat. No. 4,620,672 to Liebson, et al. discloses a system for converting a coal slurry flowable through a pipeline to a coal water mixture capable of being rendered suitable for direct combustion in a boiler. The system includes a pipeline extending from a region adjacent to a mine or source of a coal to a region adjacent to a boiler or furnace at which combustion is to take place. In the furnace region, the slurry from the pipeline is directed into a holding space, such as a pond, from which it is directed to a grinding apparatus. On the way to the grinding apparatus from the pond, a side stream of the slurry is directed through a dewatering apparatus where the concentration of the side stream is increased form 50-55 weight percent of solids to about 70-80 weight percent of solids. The outlet of the dewatering apparatus is directed back to the main flow of slurry from the pond, and the main flow enters the grinding apparatus where the slurry is ground to a particle size suitable for combustion, such as 70-80% weight percent of solids at 200 mesh. The ground slurry can then be directed into a small agitated. tank and from this tank it can be directed into the boiler or furnace for combustion.
U.S. Pat. No. 4,810,371 to Fonseca discloses a process for automating fine coal cleaning including monitoring the operation of a flotation cell for separating coal from ash impurities by automatically detecting the coal content of the tailings from the cell and controlling the supply of additives to the cell to optimize slurry coal recovery and automatically monitoring the fluid level of the coal slurry in a dewatering filter tub to control the supply of additives to the filter tub and functioning of a dewatering filter.
U.S. Pat. No. 5,236,596 to Greenwald, Sr. discloses a method and apparatus for dewatering an aqueous coal slurry which includes imparting high shear forces to the aqueous coal slurry in the presence of a peptizing agent to render coal particles hydrophobic by stripping clay from the coal particles and peptizing the clay in the aqueous medium of the slurry. The slurry is separated to recover coal particles and the aqueous medium is drained from the coal particles.
U.S. Pat. No. 5,256,169 to Roe discloses a process for dewatering and agglomerating fine coal. The process consists of treating an aqueous fine coal slurry with a chemical binding agent prior to filtration or drying. The preferred chemical binding agent is an emulsifiable process oil. Efficiencies in dewatering and in low dustiness of the treated coal are disclosed.
U.S. Pat. No. 5,346,630 to Kenney discloses a process for the vacuum filtering of coal slurries. Dewatering of a filter cake is achieved by contacting the coal with a C8-C20 aliphatic carboxylic acid or a derivative thereof, especially sodium oleate.
U.S. Pat. No. 5,476,522 to Kerr, et al. discloses a method for concentrating coal tailings and for dewatering coal products employing a copolymer of diallyldimethlylammonium halide and a vinyl alkoxysilane, preferably a copolymer of diallyldimethlylammonium chloride and vinyltrimethoxysilane as a coagulant. The method for concentrating coal tailings comprises steps of feeding the coal tailings to a thickener; treating the coal tailings with the coagulant, discharging substantially concentrated tailing; and withdrawing substantially clarified liquid from the thickener. A method for dewatering coal products containing water comprising the steps of feeding the clean coal containing water to a twin belt filter press; treating said coal with an effective amount of a copolymer coagulant of diallyldimethlylammonium halide and vinyl alkoxysilane, preferably diallyldimethlylammonium chloride and vinyl trimethoxysilane is also disclosed. The method encompasses removing water from the coal product through the addition of the subject polymer coagulant; removing the dewatered clean coal product from the filter; and withdrawing the recycled water through the filter.
U.S. Pat. No. 5,622,647 to Kerr, et al. discloses a method for dewatering coal tailings, clean coal products and mineral slurries, as well as for the clarification of water contained in coal refuse slurries, employing a copolymer of diallyldimethylammonium halide and a vinyl alkoxysilane, which is preferably a copolymer of diallyldimethyl-ammonium chloride and vinyltrimethoxysilane as a coagulant.
U.S. Pat. No. 5,795,484 to Greenwald, Sr. discloses a method and apparatus for dewatering an ultra-fine coal particle fraction forms a coal product with particles that are dilatant due to the mechanical stripping of the clay contaminants from the coal surface and the subdividing of the clay to clay platelets which are peptized to maintain discreetness in an aqueous slurry. The coal particles are unflocculated and can produce an aqueously permeable barrier on a sieve. The ultrafine coal product has an increase of 100-150 BTU per pound and when combusted reduced NOx production of 20-40% is realized. In a 15xc3x970 micron coal fraction, the sulphur content is significantly reduced.
U.S. Pat. No. 6,042,732 to Jankowski, et al. discloses a method for dewatering coal tailings, clean coal products and mineral slurries with an effective coagulating amount of a combination of a cationic polymer and a starch. A preferred cationic polymer is poly(dimethylaminoethylaerylate methyl chloride quaternary salt) and preferred starches are unmodified.
A need still exists for a further improved method and apparatus for dewatering and decontaminating coal tailings and recovering water therefrom.
A need also still exists for a further improved method and apparatus for dewatering and decontaminating clean coal slurry products and mineral slurries and reconveying process water therefrom.
It is an object of the present invention to provide an efficient and cost effective method and apparatus for dewatering coal tailings and for removing contaminants therefrom.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for dewatering substantially clean coal slurries and to remove any contaminants present therefrom.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for dewatering other mineral slurries and to remove any contaminants therefrom.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for reclaiming valuable water from coal refuse slurry ponds.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for reclaiming valuable process water from substantially clear coal slurry products.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for reclaiming valuable process water from other mineral slurries.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for reclaiming valuable land resources from land previously occupied by coal refuse slurry ponds.
It is a further object of the present invention to provide an efficient and cost effective method and apparatus for a ameliorating or eliminating any environmental risk to soils and water tables which may be presented by coal refuse slurry ponds.
It is a further object of the present invention to provide a method and apparatus for efficiently and cost effectively dewatering coal tailings and removing contaminants therefrom which is mobile and can readily be moved to
It is a still further object of the present invention to provide a method and apparatus for efficiently and cost effectively dewatering coal tailings and removing contaminants therefrom which is compact and adapted to being used on sites where the available land for such operations is limited or where such available land is located on hilly, mountainous or otherwise uneven terrains.
These and other objects of the present invention are provided by the method of the present invention, which is a method of dewatering a mixture of coal tailings, water and contaminants comprising the steps of (a) providing a tank having a base surface and introducing said mixture of coal, tailings, water, and contaminants to said tank and allowing said coal tailings to settle on said base surface, (b) removing the coal tailings from said base surface of said tank along with water and contaminants and then separating said water and at least some of said contaminants from said coal tailings wherein said separated contaminants are suspended in said separated water, (c) adding an agent selected from one or more of the group consisting of a coagulant and a flocculant to said water and suspended contaminants separated from the coal tailings in step (b), (d) allowing the agent added in step (c) to coagulate or flocculate with the suspended contaminants to form a coagulated or flocculated mass and a quantity of supernatant water, and (e) separating the coagulated or flocculated mass formed in step (d) from the quantity of supernatant water formed in step (d).
This coal slurry cleanup is unique in that it does not matter as to the size or volume of a pond. The system consists of a completely portable plant and can be moved from one location to another in a matter of days. It operates on air, hydraulics and electric generator, and can be put in very remote areas. A dredge is put into a slurry pond to pump the material. This material consists of coal, water, clay, mud, or whatever else may have been deposited. The dredge must be adequate in size to pump the volume of material and water needed to operate the plant. In most cases, a volume of 800 GPM to 1500 GPM will be required. This coal slurry cleanup consists of a method where a portable plant is assembled wherever coal slurry is found to be recoverable, normally where coal prep plants have been operating for a period of time. The slurry will then be brought to the plant and processed to where there will be a steady stream of coal from a discharge belt to a stockpile. A backflow of waste water will flow to a clarifier tank which will allow the clay, mud and other heavy materials to settle out. The heavy material will then be pumped to a hydraulic press where the water is separated from solids. The solids will then be discharged to a stockpile and the water will return to the pond for use or can be let into a water stream.
Also encompassed within the present invention is a method of dewatering substantially clean coal slurry products comprising the steps of (a) providing a tank having a base surface and introducing the substantially clean coal product into said tank and allowing fine coal to settle on said base surface, (b) removing the fine coal from said base surface of said tank along with water and contaminants and then separating said water and at least some of said contaminants from said fine coal wherein said separated contaminants are suspended in said separated water, (c) adding an agent selected from one or more of the group consisting of a coagulant and a flocculent to said water and suspended contaminants separated from the fine coal in step (b), (d) allowing the agent added in step (c) to coagulate or flocculate with the suspended contaminants to form a coagulated or flocculated mass and a quantity of supernatant water, and (e) separating the coagulated or flocculated mass formed in step (d) from the quantity of supernatant water formed in step (d).
Also encompassed within the present invention is a method of dewatering other mineral slurries comprising the steps of (a) providing a tank having a base surface and introducing said mineral slurry into said tank and allowing said mineral fines to settle on said base surface, (b) removing the mineral fines from said base surface of said tank along with water and contaminants and then separating said water and at least some of said contaminants from said coal tailings wherein said separated contaminants are suspended in said separated water, (c) adding an agent selected from one or more of the group consisting of a coagulant and a flocculent to said water and suspended contaminants separated from the mineral fines in step (b), (d) allowing the agent added in step (c) to coagulate or flocculate with the suspended contaminants to form a coagulated or flocculated mass and a quantity of supernatant water, and (e) separating the coagulated or flocculated mass formed in step (d) from the quantity of supernatant water formed in step (d).
Also encompassed within the present invention is an apparatus for use in processing a liquid and at least one solid particulate material mixed with in said liquid said apparatus comprising a tank having a front end and a rear end, a base surface and a peripheral wall, an input point positioned adjacent the rear end of the tank extending generally upwardly from and surrounding the base wall, an output point positioned adjacent the front end of the, a particle collection area positioned on the base surface beneath the input point, and means for conveying the particles extending from adjacent the particle collection area to the output point.
Also encompassed within the present invention is an apparatus for use in processing a liquid and at least one solid particulate material mixed with liquid. This apparatus includes a tank having a front rear end, a base surface and a lateral wall having an upper rim. An input point is positioned adjacent the rear end of the tank adjacent the upper rim of the tank. An output point is positioned adjacent the front end of the tank. A particle collection area is positioned on the base surface beneath the input point, and a particle conveyor means extends from adjacent the particle collection area to the output point. There is a means for separating particles and water removed from the tank, a means for adding a coagulant or flocculant to the water, a second tank directly connected to the first tank, and means for removing a coagulated or flocculated mass from clarified water.
Also encompassed within the present invention is an apparatus for reducing the concentration of a particulate material and a liquid. The apparatus has a flow cavity having an input opening for the liquid with suspended particulate material and a restricted output opening for particulate material. The flow cavity has at least one perforated wall having an outer surface from which liquid having a reduced concentration of particulate material is collected.